Adding just a little polymer to a pipe flow speeds it up by reducing drag near the wall. But the effects on turbulence away from the wall have been harder to suss out. A new experiment shows that added polymers suppress eddy formation in the flow and reduce how much energy is lost to friction and, ultimately, heat. In particular, the researchers found that polymer stress helped stabilize shear layers in the flow and prevent them from destabilizing into more turbulent flow. (Image credit: S. Wilkinson; research credit: Y. Zhang et al.; via APS)
Tag: elastic turbulence
Elastic Turbulence
Decades ago, engineers pumping polymer-filled drilling liquids into porous rock noticed sudden and dramatic increases in the viscosity of the liquid. Within the tiny pores of the rock, conventional (i.e., inertial) turbulent flow should be impossible — the Reynolds number is simply too low. Now a new experiment points to the source of the high viscosity: elastic turbulence.
To observe the phenomenon, researchers watched flow in the spaces between glass beads packed into a narrow channel. Videos of flow through one of these pores — roughly 250 microns across — are shown below. When flow rates are low (left), the fluid moves smoothly through the pore, but at higher flow rates (right), chaotic fluctuations emerge, creating the dramatic increase in apparent viscosity. In their analysis, the researchers found that the polymers’ motions generated the flow fluctuations, but most of the viscosity increase was inherent to the fluid’s movement, not to the polymers’ resistance to stretching. (Image credit: top – M. van den Bos, pore flow – Datta Lab; research credit: C. Browne and S. Datta; via Quanta Magazine; submitted by Kam-Yung Soh)
At low flow rates (left), the fluid moves smoothly through the tiny pores, but at higher flow rates (right), the polymers in the flow generate elastic turbulence that greater increases the fluid’s apparent viscosity.
